This invention relates to aqueous cleaners. In one aspect, this invention relates to alkaline aqueous cleaners while in another aspect, the invention relates to the use of these cleaners to remove resin systems, particularly dried or partially dried systems, from the surfaces of resin molding process equipment.
In the manufacture of molded plastic articles, a molding resin is introduced into a mold and cured. The mold surfaces are constructed of materials to which the resins do not adhere, in either their cured or uncured state, and thus cleaning of the mold surfaces of resin is usually not a problem. However, other equipment associated with the molding process, particularly that equipment in which the uncured resin is mixed, held or transferred, is often constructed of materials to which the resins will adhere if the resin is allowed to dry while in contact with it. Accordingly, this equipment must be cleaned of the uncured resin after the bulk of the resin has been removed from it and before the remnants of the resin substantially dry.
Various cleaners are known to be useful for removing dried or partially dried resins from various surfaces or substrates. Many of these cleaners are organic based materials, such as methylene chloride, and while often very effective, their use does pose an obvious risk to worker health and environmental safety. As a consequence, aqueous based cleaners have been the subject of study for many years, and many such cleaners have been formulated. Typically, these cleaners contain a base, such as sodium hydroxide, that will break ester and ether linkages that may be present in the resin; a surfactant or wetting agent, such as a water-soluble, alkali compatible surfactant, e.g., phosphate esters or alkyl glucosides, to solubilize lower molecular weight components of the resin, such as a plasticizer or binder; and a detergent builder, such as an ammonium or alkali metal carbonate, phosphate or silicate, to dissolve soaps formed by the base and esters or ethers. These cleaners may contain other components as well, such as sequestering agents, corrosion inhibitors, dyes and perfumes.
While many, if not most, of the aqueous cleaners on the market today demonstrate at least some degree of utility for their intended purpose, most, if not all, could be improved in one manner or another. For example, some cleaners only work well at temperatures in excess of 140.degree. F, temperatures at which cure is promoted in some resin systems, particularly catalyzed systems, and at which workers who come in unprotected contact with the cleaner could be scalded. Other cleaners lose critical components during use, e.g., through evaporation which results in either a limited period of use or a need to continually add the lost component. Yet other cleaners simply have a poor shelf life, i.e. they tend to separate into aqueous and nonaqueous fractions, or one or more components precipitate from solution, or the emulsion breaks. As a consequence, the search for new and useful aqueous cleaners continues.